Silicon carbide (SiC), also known as carborundum is an exceedingly hard, synthetically produced crystalline compound of silicon and carbon. It occurs in nature as the extremely rare mineral Moissanite. Until 1929, silicon carbide was the hardest synthetic material known. It has a hardness rating of 9, close to that of diamond. In addition to hardness, silicon carbide crystals exhibit fracture characteristics that make them well suited to abrasive product applications such as sandpapers, grinding wheels and cutting tools.
High thermal conductivity, together with high-temperature strength, low thermal expansion, and resistance to chemical reactions are some of the qualities that make silicon carbide ideal for the manufacture of high-temperature bricks and other refractories. The material is classed as a semiconductor, since its electrical conductivity lies between that of metals and insulating materials. This characteristic, in combination with its thermal properties, makes SiC a promising substitute for traditional semiconductor materials such as silicon, in high-temperature applications.
Grains of silicon carbide can be bonded together by the process of sintering to form very hard ceramics. These are widely used in applications which require high endurance, such as car brakes, car clutches and ceramic plates in bulletproof vests. SiC is used in semiconductor-based electronic devices that operate at high temperatures or high voltages, and as a substrate for LEDs. More recently, it has been used in refractory linings and heating elements for industrial furnaces, and in wear-resistant parts for pumps and rocket engines.
Silicon carbide (SiC) ceramics can also be made by a process known as reaction bonding where pure silica sand and finely divided carbon (coke) are reacted in an electric furnace at temperatures in the range of 2,200°–2,480° C. These ceramics exhibit great thermal shock resistance because of their high thermal conductivity, and make good kiln furniture for supporting other ceramics during their firing.